Independently heating or cooling several zones can be accomplished with a heat pump system having a plurality of zone heat exchangers, each operable as a condenser in the heating mode and as an evaporator in the cooling mode. In such a system, each zone heat exchanger is connected to both a gas line and a liquid line for passing refrigerant therethrough. The gas lines are connected to a common gas line manifold and each liquid line, which usually includes an expansion valve, is connected to a common liquid line manifold. Typically, the system also includes an outdoor heat exchanger that functions as an evaporator in the heating mode and a condenser in the cooling mode.
In the cooling mode, refrigerant supplied by a compressor passes in turn through the outdoor heat exchanger (giving up the heat of compression to ambient air), bypasses an outdoor expansion valve, enters the liquid line manifold, and passes through each liquid line. The refrigerant passes through the indoor or zone expansion valves and expands upon entering the zone heat exchangers, where it absorbs heat from zone air as the refrigerant vaporizes. The flow exits the zone heat exchangers through the gas lines, enters the gas line manifold, and returns to the compressor, completing the cycle.
In the heating mode, the flow is reversed, however, the zone expansion valves are now bypassed and the outdoor expansion valve becomes active. Furthermore, the zone heat exchangers provide heat to the zone air while the outdoor heat exchanger absorbs heat from the ambient air.
When the temperature conditioning demand is satisfied, the appropriate zone heat exchanger is deactivated by closing off the refrigerant flowing therethrough. This poses no problem in the cooling mode, because the expansion valve on the liquid line can stop the flow entering the heat exchangers. Any liquid refrigerant inside the inactive heat exchanger will vaporize as it is exposed to the compressor suction pressure through the gas line and gas line manifold.
However, deactivating a heat exchanger during the heating mode poses a problem. When only the zone expansion valve or a liquid line solenoid valve is used to stop the flow, vaporized refrigerant will condense and eventually accumulate to a point where it floods the inactive heat exchanger. This deprives the remaining active system of the refrigerant needed to function properly.
It is possible to solve this problem with an upstream valve on the gas line of each zone heat exchanger. But these valves, being disposed on the inherently large diameter gas lines, must also be relatively large and therefore, more expensive and prone to leak. In addition, the pressure drop across valves used for this purpose is typically less than 30 psi which makes it even more difficult to obtain a positive seal. Nevertheless, this method as disclosed in U.S. Pat. Nos. 3,916,638; 4,299,098; and 4,399,664 is still used.
Another solution, as described in U.S. Pat. Nos. 3,994,142 and 4,528,822 includes a large refrigerant holding reservoir relied upon to maintain a sufficient refrigerant charge in the system. Although appropriate in large systems, its complexity and cost make this method impractical in smaller systems.
In view of the above, it is an object of this invention to provide a relatively simple and inexpensive method of preventing flooding of an inactive heat exchanger that is interconnected in parallel with a plurality of other heat exchangers.
Another object is to deactivate a zone heat exchanger without using a valve on the heat exchanger's gas line.
A further object is to maintain a sufficient refrigerant charge, without using a holding reservoir, to enable proper operation of a heat pump system having a plurality of independently activated zone heat exchangers.
These and other objects will be apparent from the attached drawings and the description of the preferred embodiments that follow below.